Trying to track down a horror film, likely from the 80's or late 70's, that my babysitter's son traumatized myself and my sister with back in the early 90's. It was a zombie film, I think, or with some similar kind of ghouls and monsters, and everything I remember has a very strong red tint over the scene, strong reds and blues - the scene that sticks out in my head is a girl trying to hide in a bathroom, locking herself into a toilet stall and sitting on the bog but a zombie smashes his way up from the toilet and grabs her. This ring any bells for anyone?

some similar kind of ghouls and monsters -the scene that sticks out in my head is a girl trying to hide in a bathroom, locking herself into a toilet stall and sitting on the bog but a zombie smashes his way up from the toilet and grabs her. This ring any bells for anyone?

The small monsters, and the toilet description reminds me of Ghoulies 2.

You're not thinking of "Willies" are you? Your description sort of reminds me of the scene where the kids are at school and the monster is in the bathroom stall. Pretty sure the monster ends up killing the teacher and pulling her through the roof.

I checked all of these, no such luck unfortunately. The thing I remember most aside from the zombie-monster-things and the toilet is the red filter over everything, very harsh reds and blues over everything, possibly with very heavy metal music. Are there any other movies or TV shows or music videos this reminds anyone of?

Strong reds and blues and discordant (even metal-like) music sounds very much like something by Dario Argento. While the scenes don't match your description, there are "monster" attacks like this -- color and sound wise -- in both SUSPIRIA and PHENOMENON.